In its classic form, a cable television system carries information in only one direction, from the cable system headend to the individual user. The user's interface to the system generally includes a receiver, for example a television or a stereo. During operation, the head end transmits television or stereo channels simultaneously. In general, the user has no influence on what is transmitted and could only choose among the channels the headend was transmitting.
More recently, data communication between a cable headend unit and a subscribing set-top box has been used for a number of two-way communication functions including ordering pay-per-view programming. Additionally, cable television networks have become available for the transmission of data. A typical cable television system can carry many television stations, which are the equivalent of a large amount of data (high bandwidth), simultaneously. Because of the increasing availability of cable television infrastructure, using television cables as the medium for computer data networks has the potential for giving users high bandwidth at a reasonable cost. However, a cable network typically requires a number of enhancements such as a cable modem and a network protocol to assure that each user receives the information they require without interference from other users.
While the addition of a cable modem to each set-top box effectively facilitates two-way communication between a set-top box and a headend unit, the added cost of a cable modem to a set-top box is often prohibitive. Moreover, consumers already own a number of set-top boxes that are not equipped with cable modems.